Coupling for coaxial cables



March 2, 1954 w 11 HOPE 2,671,127

COUPLING FOR COAXIAL CABLES mum/011M 71: P

BY M Patented Mar. 2, 1954 2,671,127 COUPLING FOR COAXIAL CABLES William D. Hope, Cambridge, Mass., assignor, by

mesne assignments, to

the United States of America as represented by the Secretary of War Application February 18, 1944, Serial No. 522,947

11 Claims. 1

The present invention relates to a detachable coupling and is particularly directed toward a coupling for use with coaxial cables used in high frequency communication equipment.

The principal purpose of the present invention is to provide a readily detachable coupling which will at the same time be effective to seal the intericrs of the cables at the joint. This feature is important where equipment may be subjected to external pressure subatmospheric pressures. It is desirable that air pressure within the equipment, including cables, be maintained at or above atmospheric. This provision is necessary to maintain the in.- sulating and dielectric qualities of air as well as to prevent moisture condensation from repeater pressure changes. i

The coupling also maintains the cables against deformations tending to vary the transmission characteristics, as well electric constant of air between the axial and coaxial conductors which would follow variation of pressure within the cable, with accompanying ineffectiveness and distortion, if not inoperativeness of a receiver unit.

Another object is to provide a coupling which is readily attachable and detachable, thus avoiding difficulties attending use of the usual sealed joints.

Other features and advantages of the invention will become readily apparent as the description proceeds, reference being had to the accompanying drawing wherein a preferred form of the invention is shown. It is to be understood, however, that the drawing and description are illustrative only, and are not to be taken as limiting the invention except insofar as it is limited by the claims.

The accompanying drawing is a longitudinal section of the coupling.

Referring now to the drawing, a fixed cable or other device is indicated at I. Inc device l terminates in a sleeve 2 of brass or other suitable metal, which is sealed to or integral with the device and is provided at its outer end with external threads 3. The inside of sleeve 2 has a flared tapered surface or contact seat 4 within its outer end and a planiform end seal face outwardly of the seat 4. A conductor 5 is disposed centrally within the sleeve 2 and is spaced and supported therefrom in any suitable manner.

A flexible coaxial cable which is'to be coupled to the device I is indicated at [0. The cable it includes a central (axial) conductor H, a spaced outer (coaxial) conductor and electrical sheath variations ranging down to w as by variation of the di- I2 and an external layer of insulation l3 as a dielectric hermetic sheath. The outer conductor I2 may be of woven or braided copper wire construction. The insulation sheath l3, which overlies the outer conductor, may be rubber or other plastic material.

An annular metallic draw-sleeve I5 is disposed about the braided part of the cable ll] near its end, and a wedge portion [8 thereof lies between conductor l2 and insulation I 3 to enlarge the latter. Ihe sleeve I5 is thick at its intermediate region it and tapers down therefrom toward either end as shown at I! and I8 forming sharp annular edges at the extremities. An annular flange It projects from the thick intermediate region it. Sleeve l5 may be secured to the conductor 12 in any suitable fashion, as for example with solder. The sleeve l5 may be termed a floating sleeve, to indicate its relation to the two pieces 2 and 25. Free end 20 of the conductor I2 is turned back so as to overlie the tapered surface ll of sleeve It. A part 2! of the insulation l3, which is separated from the conductor 12 by the sleeve I5, overlies the tapered surface 18 and abuts and covers one side and the periphery of the flange 19 of the sleeve.

Another metallic sleeve member or coupling 25 is disposed revolvably about the cable I t inwardly of its end. This sleeve has a smooth cylindrical bore at its outer end and a portion 23 of its interior surface flared toward the joint to cooperate with the tapered surface ill of the sleeve l5. Its larger part is of substantially less radius than the flange. The sleeve 25 also has an enlarged coupling portion 27, which is interiorly of greater diameter than the flange l9 and internally threaded at 28 to engage the threads 3 of the first sleeve 2. It has a planiform shoulder 22 normal to its longitudinal axis, extending from the end of the flared part 26,. and opposed to the outer face of the flange IS.

A light metallic ferrule sleeve 29 lies between insulation is and sleeve 25 to permit the latter to turn freely as the coupling is assembled.

A rubber or leather annular gasket 35' is disposed within the coupling portion 2'i and is compressed against the planiform end of sleeve 2 and flange [9 when the sleeves 2 and 25 are screwed together firmly.

This clamping action causes a partial extrusion of the insulation 13 toward the gasket 35. and so effects a hermetical seal there at the same time that the gasket becomes sealed against the planiform end seal face of the sleeve 2. The gasket serves as an extension from the sleeve 2 homeon the sleeve 2,. with the shoulde --.the nangeie and the gaskettfi pomp/res d,

,wou-ld stillbeaspace. between the tapered p s .18 Bind-125 though measuring ,much less ra lly than "the initial thickness or" the, insulati jNormally, .however, the space, between the .shoulder a22and flanges if} is not ,clo d 1 e upl n is comoletedalth ush h stis thicker than when compressed, it, etc sbe extruded slightly toward the lei .=sleeve;25 -is.screwed home oii'ih gfil t slipped .on to ,the cable, a portion of in gagement is effected, and as the sleeve Et-is' drawn onto the first sleeve 2,,the. ferrule as is carried therewith and the portion ii of the insulation i3, lying between. the inner end of ferrule 23 and tapered surfaceil, is com pressed and flows into the annular space between the three sleeves against {the rubber-gasket and against flange it. The flange cooperates with sleeve 25 to force insulation 3% against the end face of sleeve 2 and press the sleeve it with its. associated turned basis. endiicto ssain th seat sin sleeve :2 of theai iiitine ab e and- .E .last function insures ood ;m.eta i I e the .QGWO outer condu tor o th cables. The cables are coupled in a pres proof manner when the displaced insulation.

1-.thegssket3t. to ether completely on the annular space 35.

:-'-Th-e inner conduct rs .5 a d i a be ic at 3:1 iniany suitable manner such as cooperating .ipinand socket. n plastic mater-nits be forced :into the cables at the joint, if desired. Or spaced-beads may be relied upon if desired.

- -llt .should be noted that the intern l t pe par-11:26 of the sleeve. 25 is of sufficiently greater -;.diameter than-the lon tapered end it off the sleeve 18, that if the sleeve 25 were sc ewed hen at 2i is considerably compressed and displaced.

It will .be understood that. init a sii lfiei 1 '3 l the conductor I12 isptightly clampe a a n -ti seat l.

In the preparationpithe fiableen 52 th -.-sleevei2 and then the ferrule 29 ha ng been .tion is may he removed was to leave hi. end

of. the external conductor iii exposed fcr .is- .:.tance sufficient to permit the part i 8 of the f oat- ,ingsleeveiB to be inserted aroundthe-conductor 1'2 and forced into the end of the cable pledging insulation i3 outwardly until the flange-i i is vat or partly under the insulation i3 and thecon- .ductor-iiprojects ,fromunder-the sleeve it. The

=flange. The coupling is then ready yfQlT connection. First a plastic insulating material is pressed into the spaces around the axialeonductors sandal! inconductor-sleeve 2 and con -ductor l2, button or otherspacer supports inserted.

The plastic :32 is applied so that whenlthe sleeve l=5 and conductor .12 are drawn upsto fiche mres d conductor 2, the applied plastic in the cable ends will meet and join as an integral body without an apparent joint at the junction thus formed. The plastic 32 may extend a short distance into the conductors 2 and i2 sufficient to assure its stability, and other supports used in the remainder of the conductors 2 and i2 in accordance with common practices. The conductors ii and H being then conventionally connected, the

sleeve 25 may be drawn over the junction and screwed home on the conductor 2.

.When, in the preparation of the cable end iii and application of the sleeve iii, the latter has been positioned with its flange slightly under the insulation 13, 1 the subsequent coupling movements and-function of the coupling parts when sleeve .,25 is screwed home continue until the end portion ii of the sleeve i5 presses the overlaid returned extremity of the conductor 32 tightly against the seat i. An excess of the material it .may by that time have been compressed and displaced from between the sleeves i5 and vin become conne e o amaX m i -oi th space 35, any continuing displacement o i naterial i3 thereafter will be backward toward the outer end of the fer-rule. fifhe jointhetween the sleeves 2 and 2 5 and the intervening seal by gasket 35 and insulation is attained as Ides ed and shown within v the space j-lii, will ,be an equivalent of a hermetic ,sealand there or may he termed hermetical. it is moisture well as water-prooi and gas tight and l-l insure the preservation of astable pressure in th standing between the coaxial conductors when spaced supports are. used with intervening .clearanees s mmonly act ed; lo ring-0W electric value and liability of disturbance of transmission characteristies ,at high altitudes are thus guarded against, the 'f1rstof which is essential in all installations, and the latterv essential in many.

In the closing 'movemen-t oi the sleeve: 25 on the sleeve 2, theliared pflitionit of the ferrule i pre d a ain t th out d :we e iii-ii 2| of the insulation, so that thelatter is comd tends to be drawn alongwith the ferrule and sleevefiio'. This results in a placement of a portion of the insulation it as the flange is encounters and compresses the gasket 33, with the result that some of the insulation is extruded into the space 35 before the shoulder 22 an a u d t dens 1. 9 a n t as e 3%. The opposing tendency ,Of thegasiret-to at the same time results in a very tight joint between the gasket and insulation, and between the gasket and the planiform endiace oi the sleeve 2 outwardlyof theseat l.

In case it becomes necessary to disconnectthe coupling, the sleeve .35 is unscrewed frornsleeve 2, and drawn back, afterwhich the two cable elements are pulled apart, breaking the material 32, which may be reconnected by heating, if a therm plast c, or b a li at on o i hm t r and/or solvent in the case of rubber lorruober cements. A seal within the conductors .2 and it at the joint is not essential in most cases, and head or other inserted spacers may be preferred.

From the above .'des cri ption, it will heseen that the present invention provides a readily attachable and detachable cable which. seals the cables in a pressure-proof manner at the joint. Also the current carrying metalisuriace, efthe outer surface of the -cent ral.conduct or and inner surface of outer conductor, maintain. their eometricalccii ieiiriiientend t m intain the characteristic impedance of the cable at a uniform value throughout the coupling.

Having thus described the invention, what I claim as new and desire to secure by Letters Patent is:

l. A coupling for coaxial first and second cable ends and the like, at least the second one having a plastically deformable hermetic sheath surrounding the outer conductor of the cable, a first sleeve constituting part of a sealed first cable end, a second sleeve disposed slidably on the second cable and around the outer conductor thereof, said second sleeve having an annular first wedge end inserted longitudinally under the said hermetic sheath and having an opposite second annular wedge end tapered inwardly to a sharp draw edge, the end edge portion of the underlying outer conductor of the second cable end being recurved over said second annular wedge end, the first sleeve having an annular conductor seat on its extremity to oppose the draw edge of the second sleeve and bindingly engage said recurved end edge portion of the outer conductor of the second cable end, a third sleeve around and slidable on the sheath of the second cable end interiorly taper-shaped around the first wedge end of the second sleeve to compress the interposed part of the sheath lying over the first wedge end, a part extended longitudinally from the first sleeve toward the third sleeve having an annular seal surface spaced from and around the second sleeve extending radially outward from near said recurved part of the outer conductor and positioned to receive in sealing engagement thereagainst annular insulating material compressed by material of said hermetic sheath extruded from between the second and third sleeves, and means to draw the first and third sleeves toward each other longitudinally and to couple the same.

2. A detachable coupling for flexible coaxial cable having an external plastically deformable insulation sheath, an outer flexible conductor thereunder and an inner conductor, said coupling comprising an outer coaxial conductor first sleeve and a first inner conductor end together constituting a first cable end, said coupling also comprising a second cable end of flexible coaxial cable and having a second sleeve slidably engaged around the outer conductor thereof, said second sleeve having an external flange therearound and a longitudinally extended tapered end for insertion between the said outer conductor and sheath of the second cable end and having also an oppositely projecting externally tapered conductorclamping end, the end of the last named outer conductor being turned back on the said conductor-clamping end of said second sleeve, a third sleeve over said second cable end and overlying said second sleeve, a hermetic gasket disposed about the said conductor clamping end of the said second sleeve between the first sleeve and said flange, means on said first and third sleeves for coupling and drawing said sleeve telescopically together including a part on the third sleeve concentrically encircling said gasket and in concentric spaced relation to the periphery of said flange to form an annular space around said flange and containing the gasket, and adjacent said conductor clamping end part of said second sleeve, said second and third sleeves constructed to coengage the sheath therebetween and compress the material of the sheath so that it will fiow into and fill the said annular space between the first and third sleeves around and past said flange until compressed as a hermetic gasket part in said annular space when the first and third sleeves are drawn together, whereby the cable ends are joined in a pressure proof manner hermetically sealed across the joint by the external insulation of the second cable end, and means for connecting the said inner conductors together.

3. In a coaxial cable coupling for first and second cable ends having respective axial conductors and respectively first and second coaxial conductors, means to couple the axial conductors, means to couple the coaxial conductors including an inner coaxial-conductor-gripping sleeve slidable to a gripping position on the second coaxial conductor, the first coaxial conductor constituting a sealed part of the first cable end for confining gas under pressure therein and having a coaxial annular conductor end seat opposed to said coaxialconductor-gripping sleeve to coengage an interposed end part of the second coaxial conductor and having also an annular concentric end seal face radially outward of the said seat, the second cable end having a plastically deformable hermetic sheath over the coaxial conductor therein next to said coaxial-conductor-gripping sleeve, the extremity of said sheath annularly and concentrically enlarged in diameter, the said coaxial-conductor-gripping sleeve being enlarged toward the first named coaxial conductor adjacent the enlargement of the sheath, an external coupling sleeve surrounding and snugly fitting slidably on the hermetic sheath of the second cable end and interiorly taper-enlarged toward the first coaxial conductor around and beyond said enlargement of the hermetic sheath and around and in spaced relation to the enlargement of the coaxial-conductor-gripping sleeve at least to the said end seal face of the first coaxial conductor so as to form an annular seal-receiving space within said coupling sleeve extending to said end seal face, said coupling including means to draw said external sleeve toward the first coaxial conductor so as to compress and extrude material of said hermetic sheath against the enlargement of the said gripping sleeve and beyond in the seal receiving-space, and an hermetic seal in said space against said end seal face of the first conductor including at least in part material of said sheath extruded into said seal receiving space, whereby the pressure of said extruded material will operate the coaxial-conductor-gripping sleeve and press said hermetic seal against said end seal face to form a hermetic seal across the joint between the cable ends.

4. In a coupling for insulated flexible coaxial cables, a conductor sleeve of a size to align with an opposed end of an outer conductor of a flexible coaxial cable to form an interiorly flush continuation thereof and formed with a seat to coengage with an outturned end of such outer conductor, a second sleeve having separable connection with the conductor sleeve and having an extremity restricted to engage slidingly around a plastic insulation sheath of an insulated flexible coaxial cable and having an enlarged concentric annular chamber therein toward the conductor sleeve, and a clamping sleeve separate from both the conductor sleeve and said second sleeve and relatively and freely movable within at least the second sleeve, the clamping sleeve having a cylindrical interior of the same diameter as the exterior of the said outer conductor, one end of said clamping sleeve being thinned for insertion under the insulation of the flexible coaxial cable and over: the outer conductor thereof and having an a ser-gm? annular iintermediate .:en1arge1:l;; -.portion:;;ofiless 1 di ameteri than-said chambertbuttarrangedr totproset: radiallyrthereintoza: distanee,-i-. wherebyia portion; .of said. insulation ssheath zoverlying-v athe :clamp'mg sleeve may; be: compressedabetweenlthe second: namedz sleeve 2 and. the; said enlarged: portion of the.clampingsleeve; so asttmnove the latter; towardxthefirstznamed:sleevesandiintm clamping: engagement with :anoutturnedsend portion of agcoaxial conductor: againsttsaid seatonlthe first named sleeve.

15. Inascouplingjforrafflexibleitransmissiondine relatively slidablesparts, oneuof. said separable parts at least constructedi'and; adapteduto :telescopioally receive-at-rleast aaportion'cof said transmission line cable/and havingtspaced therewithin a relatively movable externally tapered-1 clamp sleeveiof an inner-diameter closelyl'approximating the external. diameter sofa said transmission .iline outer conductor;andzinsertable between saidvainsulation sheathand saidlouter conductor, said firstnamed sleeve means havingnn annular enlarged chamber with clearance around sthe larger diameterlportion;oisaidclamp.sleeve, said-one at least part of :saidseparable and relatively slidable parts shaped withvsaidi taperedclamp sleeve forgclamping the end' portion of the saidiinsulation sheath therebetween, holding meansdn cluded in saidfirstznamed sleeve means, theother of. said :separableyand relatively .-.slidable parts of said first. :nained sleeve: means and said. clamp sleeve havingopposedicooperative clamping. porions to receive and' clampi 'therehetween an end edge :portion of said.transmissionsline: outer conductor; means to:;-drawzt-he V-said separable :par-ts of the first named-vsleeve meansitogether and axial ,conductoricoupling means-spaced within said coupling for coupling with said transmission line inner conductor.

6. In acoupling for flexible coaxial cables having :plastically deformable external sheathainsulation; a cable end having a sealed-on terminal concentric conductor sleeve formed with .a seat ior ooengagtngan opposed coaxial outer conduetor. end of ailexible coaxial cable a nut sleeve having;threaded,engagement with the said '"ter minal conductor sleeve; and having arilongit a dinallyand taperingly restricted distal portion adapted at its smallel -partto en age slidmglvon the plastically deformable insulation sheath of an insulatedflexible'coaxial cable, and an intermediate rigid sleeve spaced movably within one at least of the first twosleeves, havingan interior diameter the same as that of the outer diameter of the said outer-eonductor of the flexible coaxial cable-to be connected, and having a taperedend insertable between the end portion of i said sheath insulation andsaid outer conductor and-having an intermediate external enlargement therearound the opposite end of the intermediate sleevebeingshaped to receive end portions of said outer conductor of the flexible cable end, and tocoactu-with said seat to clamp the interposed end-portions off-said outer conducton-said nut; sleeve being formed with an annular chamber space-concentrically therein extending from the larger'part of said taperingly restricted portion thereof to slidingly receive the said intermediate sleeve, said restrictedpart of the nut'sleeve and the tapered outerend of I said intermediate sleeve :being shaped andzpositionedato-zcompress an int'erposed :part 4 of ;said insulation zlsheath nwh'en zthe .first (.named sleeve and nut-sleeve: are drawn -':to-

gether, so: as;to:zextrudezthe: sheathimaterialalongitudinally into said space and against the cen- ;largement ;of .thetintermediate sleeve sand to therebyzgmovmthellatter ,lntoiclamping; relatio'nito :said :terminal conductor sleeve upon .an interposed;extremity. oizsa-idouter conductor of flexible coaxial, cable, and 5means1to :form '3' coupling with the inner .conductor of such flexible co axial cable.

.7. .An automatic. hermetic :sealand separable lconplinglifor. flexible-rcoaxial 'icablesin which the cable comprises an axialconductor, anoutencoaxial braid conductor spaced ,therearound and an external plastically ade'formable hermetic sheath linsulation; .-said coupling oomprisingoan inner axial conductor zeonnector,.:an outer concentric conductor body having a bore iclosely zap-- proximatingthe' inner diameter of said outer conductor of the cable. having an inner annular gen'd seat extending from :said. bore, a cir 'cum'ierentially continuous cable encircling sheathecompressing clamp sleeve opposed coaxiallyto said bodyand vconioallymeduced at Iits .extremityrto pthenonnal outside diameter 'of I the cable, an'interiorly.cylindricalfloatingxsleeve longitudinally. slidable within :said clamp. sleeverat least and having an enlarged part'towardthesaid bodyandofless diameter'thanvthe 'interior oi said clamp, sleeve to form can extrusion gpath therearound for. sheath insulation: compressed bysaid clamp sleeve, andin the path of relative longitudinal movement of the clamp sleeve and being also tapered towardrthe-rlatter to a wedge shape for insertion between the end-of :saidsheath and said outer conductor of @a cable end and having anopposite braid-clamping end matedto saidend seat, draw means to draw said :clamp sleeve and .saidbodytogether around the floating sleeve, said floating sleeve :and sheath compressingqpart of the clamp sleeve being vatiablyspaced mutually andclongitndinallyiinz tandem relation and having initial effective sealing :and clamping positions relative'to an interposed part of-said sheath, the said-initialiposition of the floating sleeve being short of its iull clamping :positionin relation to saidue i seat and :an interposed braid end, said clampingxsleeve having also :a further inwardly spnced full clamping position inyrelation to said floating-sleeve and interposed sheath material, and'rth'e-floating sleeve having a further full clampinguposition'ain relation to the interposed braidend and said end seat whereby when applied toa cable end: and said draw means 0perated'the sheathwillbe compressed against said floating sleevebyrthe clamp sleeve'and the floating sleeve moved a distance" thereby and; finally hardpressed againstthe braidend by finalmovementof the clamp-,sleevasaid coupling including an elastic compressible hermetic sealing annulus outwardly ofsa'id end seat confined between the said body and-extruded "material around the lioating sleeve at the last-namedpositions of'the parts.

8." In acoup'ling for transmission line cable and the "like having an outer-tubular 'fie'xflole conductor and a pla'stically deformable hermetic insulation covering; a' hollow cylindrical-conductive coupling body having onits end closely around theinternal face of the body'an'annular clamp seat for-an end'portion of "saidouter conductor and having an annular seal face'outwardly'of "said seauwithin the coup'ling to "receive "an annulus of insulation thereagainst, means for securing the outer conductor of said line to said body to form a smooth continuation of said outer through and adjustably connected to the body for longitudinal movement thereon, and means defining line insulation covering clamping means and an insulation receiving space extending to said seal face around an inserted end of said line within the coupling, the last named means comprising annular radially spaced opposed clamp surface parts at the outer end portion of the coupling within the holding member, the inner one at least tapered toward said end and having a sharp outer edge insertable in the line end between said insulation and said outer conductor, said holding member including the outer clamp surface part and being interiorly shaped and extended as a terminal continuation of the outer moved inward toward the body and the insulation material extrudingly displaced longitudinally inward into said space and reformed as a terminal gasket part integral with the line insulation in said space, said space being of greater diameter than the thickest part of said sleeve, so as to accommodate a part of said insulation material around and past said thickest part and having a radial extension to receive a portion of said insulation material extruded into said space from between said clamp surface parts so as to form a key element and seal to anchor the insulation of the line to the coupling until said holding member is withdrawn.

9. The structure of claim 8 wherein said inner clamp surface part within the holding member is a discrete sleeve-like member initially in a floating relation to said body and holding member, and having a conductor-clamping end face at its inner thicker end aligned with said seat and shaped to engage and clamp the extremity of the said outer conductor of an inserted line end against the said seat under pressure of said insulation against the floating annular part when said holding member is moved inward on the body into compressive engagement with the said insulation of the line overlying the inner clamp surface part.

10. The structure of claim 9 wherein said discrete member has a peripheral flange at its inner end to receive thereagainst material of said insulation extruded from between the opposed clamp surface parts, whereby the resultant of hydraulic forces effective through the insulation material is increased at the clamped part.

11. In a coupling of a coaxial type transmission line having an inner conductor, an outer concentric flexible conductor and an insulation covering of plastically deformable material as a sealmg sheath around said outer conductor; a coudiameter of said space sufficiently to accommodate a part of said insulation covering around said floating annular member at its thickest part, said holding sleeve having an internal sheathclamping face bounding a part of said space, opposed to and complementary to said tapered surface of said floating member and having a sheath-fitting outer terminal part extended from the end of said internal sheath-clampin face a distance for engagement around the insulation covering of the line beyond said complementary sheath-clamping face over a substantial distance, said coupling including means to secure the said holding sleeve in adjusted positions on said body in clamping engagement with sheath material of the inserted end of the line interposed between said clamping faces and extruded forwardly into the said space around and beyond said major diameter of said floating annular member, to be compressed against the latter and bear it against the extremity of the said outer conductor interposed between the iioating member and said body, and whereby the extruded sheath material is compressed toward the said body and confined as a part at least of a hermetic seal between line insulation and coupling body.

WHJLIAM D. HOPE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,060,600 Jamieson et a1. May 6, 1913 1,223,444 Tanner Apr. 24, 1917 1,497,002 Sanderson June 10, 1924 1,718,817 Greene June 25, 1929 1,959,442 Paulson May 22, 1934 2,173,643 Moser Sept. 19, 1939 2,181,860 Adkinson Dec. 5, 1939 2,287,135 Robertson June 23, 1942 2,296,766 Bruno Sept. 22, 1942 2,425,834 Salisbury Aug. 19, 1947 2,449,983 Devol Sept. 28, 1948 FOREIGN PATENTS Number Country Date 112,951 Great Britain Feb. 7, 1918 489,510 Great Britain July 28, 1938 

